Rare earth magnet is manufactured by finely dividing an alloy or alloys based on rare earth metals and transition metals, followed by compaction and sintering. If desired, the sintered block is cut, ground or otherwise machined into a magnet product of the desired shape and dimensions. Since rare earth magnet can be oxidized at elevated temperature, with its properties degraded, the machining operation is carried out while cooling, typically using a machining fluid therefor.
The machining fluids are generally divided into two types, the fluid of water-insoluble type used as such for the main purpose of lubrication and the fluid of water-soluble type used after dilution with water for the main purpose of cooling. Nowadays, water-soluble fluids are most often used from the considerations of operation efficiency and fire hazard. In the machining of rare earth magnet, water-soluble fluids are used from the considerations of operation efficiency and safety because the constituent rare earth metals are susceptible to oxidation.
Even when machining is performed using a water-soluble fluid for cooling, chips are heated due to the heat generation associated with machining. The chips become so reactive at high temperature that they may be oxidized with water or airborne oxygen, forming the oxide and/or hydroxide of rare earth metal. While chips resulting from machining are generally separated from the water-soluble fluid by a settling or magnetic separation method utilizing the high specific gravity or magnetism of chips, such a method fails to separate particulate oxide and/or hydroxide. Particulates are kept suspended in the fluid while the fluid is circulated. Thus the fluid becomes turbid. Worse, particulates deposit on the surface of a workpiece, adversely affecting the quality of the workpiece. Also some particulate oxide and/or hydroxide can form a hydrophobic salt with an organic acid present in the machining fluid, which salt is taken into bubbles generated during the machining to increase the stability of bubbles. As a result, more bubbles are generated rather than being extinguished, and eventually overflow the machining system or fluid reservoir, substantially detracting from operation efficiency and safety.
It is believed that the problem is overcome by separating particulate oxide and/or hydroxide out of the system as soon as they are formed. If this is done by filtration using a pressure filter, the process becomes complex and the initial investment is increased. It would be most desirable if particulate oxide and/or hydroxide can be separated together with chips using a simple separator such as a settling separator or magnetic separator. Regrettably no effective method is currently available for such separation. In conjunction with the cutting and grinding of rare earth magnet using water-soluble fluid, no patent documents refer to the turbidity and bubble generation of the fluid. As long as the inventors know, there are available no patent documents to be incorporated herein by reference.